Out-of-band emissions and non-perfect receiver selectivity can result in adjacent channel interference (ACI) between consecutive frequency channels in 3G networks. When the level of ACI is high compared to the wanted signal power, 'dead zones' are formed in the network. However, the size and location of the dead zones are hard for network engineers to predict, as they depend on the configuration and loading of the adjacent network as well as of their own. We show the benefit of using an advanced 3G planning tool to predict dead zone formation accurately. The same tool is then used to quantify the benefit of various mitigation techniques. In particular, we identify how close the base station sites of the adjacent networks must be to avoid dead zones, and show that introducing a guard band between operators is unlikely to provide an effective solution.